In recent years a broadband service with continuous connection has come of age, enabling a user to utilize an access network for transferring high throughput traffic.
Meanwhile, capacity expansion in a backbone network does not catch up sufficiently with the abrupt traffic increase. From the viewpoint of efficient network usage, a backbone network bandwidth is normally shared by a plurality of users. For this purpose a concentrator is provided in a network to concentrate packets for multiplexing. Furthermore, it is required to install packet multiplexing equipment to enable efficient and fair bandwidth control fit for traffic characteristic.
As a bandwidth control method employed in an Ethernet LAN, a method called CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used.
The CSMA/CD is illustrated in FIG. 1. Any transceivers (TRC1-TRC5 . . . ) being connected to a cable 100 always supervise a carrier signal flowing on cable 100. When either one station is in transmission (from station A to station D in the example shown in FIG. 1), other stations are controlled to postpone the transmission therefrom and to start transmission when each transceiver concerned indicates a condition that no signal is flowing.
Accordingly, in CSMA/CD, it is required to detect whether or not other terminals are in transmission conditions. For this purpose the network is required to provide a broadcasting function. There is a problem that a portion of bandwidths is consumed to perform this broadcasting.
Also, in this CSMA/CD, transmission-timing control for transmitting a packet is necessary on each terminal side. Therefore, when this method is employed straightly in a public network, ordinary good users cannot be protected from a user transmitting extremely large amount of data in high speed with a malicious intent, causing a problem that fair bandwidth control is impeded.
Meanwhile, as a method for bandwidth control for the public network, there has been used UPC (Usage Parameter Control) as well as the integrated and differentiated service. Such a method is employed in concentrators 2-1, 2-2 shown in FIG. 2. In a network shown in FIG. 2, a packet is transmitted from a terminal 1 located in user premises through an access line. The packet is then multiplexed by a multiplexing controller 10 provided in each multi-stage concentrator 2-1, 2-2. Thus the packet reaches a contents server and a central office (CO) 3 connecting to the Internet 4.
Packet-multiplexing controller 10 provided in such concentrators 2-1, 2-2 classifies traffic flow on a connection-by-connection basis in a packet classifier 11, as shown exemplarily in FIG. 3. Further, traffic pattern (classified by peak cell rate, average cell rate, burst length, etc.) is specified for each arriving traffic on a basis of each connection, flow, and class by presetting in a polisher 12.
Input packets from a plurality of terminals PC1-PC3 are classified in packet classifier 11 into a plurality of traffic flows. These classified traffic flows having arrived from each plurality of users are input to a marker 13. At the same time, according to the previously specified traffic patterns mentioned above, traffic flow rate is monitored in polisher 12.
The monitoring result of traffic arriving from each user by polisher 12 is forwarded to both marker 13 and a discard controller 14. Marker 13 replaces a packet header according to a policy and a traffic flow rate, to forward the packet to a corresponding queue (waiting queue) 16.
Discard controller 14 discards a packet violating the specification of traffic flow rate monitored in polisher 12. Also, discard controller 14 discards a packet depending on the length of queue 16. In addition, scheduler 15 controls to read out queue 16 based on the rate, priority, etc.
As can be understood, the concentrators according to either UPC (User Parameter Control) or the integrated and differentiated service method require a substantially large amount of hardware for monitoring traffic pattern. Also it is required to reserve resources necessary for monitoring in advance.
In case of connectionless communication such as continuous connection, it is required to maintain the number of resources more than the number of users or the maximum number of packet-flows transmitted from each user. This causes a problem of additional increase in hardware, which results in cost increase.
It is currently under study to introduce competition control between quality classes by providing an individual queue on each quality class basis. However this competition control method is effective in possible competition between different quality classes only. The quality class is identical so far as traffic flows within the best-effort class, which presently shares the largest portion among ordinary users. Therefore for such traffic a service control method in order of arrival must be applied, such as a simple FIFO (first in, first out) service method, and therefore it is hardly possible to achieve fair bandwidth control.
Furthermore, data transmitted from one user are generally constituted by a plurality of packets. When concentrator 2 discards packets on occurrence of competition, as shown in FIG. 4, packets from each plurality of users are randomly discarded.
Namely, in the example shown in FIG. 4, discarding packets randomly in the event of competition makes it impossible to receive data thoroughly even from a single user. As a result, packet data from all users must be retransmitted. This is not efficient usage of a network because large retransmission overhead is produced.